Modern aircraft provide passengers a variety of entertainment programs, including movies, science features, advertising, news, music and other types of video and audio programs. However, all of these programs are pre-recorded (usually on magnetic tape), sometimes days or months prior to the commencement of the flight. As a result, while today's airline passengers are increasingly able to take advantage of high-technology services, such as in-flight telephone calls, they are cut off from live news, sports events and other events that occur during the course of a flight. Thus, it is quite common to witness airline passengers rushing to the nearest television set immediately after their flights have landed at an airport, particularly if a major news or sports event is taking place. In some cases, even that option is not available because the event is taking place at a distant location and is not of local interest at the passenger's destination.
Although aircraft are capable of receiving radio and television broadcast transmissions from terrestrial sources, this is not a practical way to provide real-time news and entertainment programs to airline passengers. One problem is that the effective range of most commercial radio and television broadcast stations is limited to a distance on the order of 100 kilometers. For a turbine aircraft flying at a speed in excess of 750 kilometers per hour, it is apparent that the aircraft will be within range of a terrestrial broadcast station only for a short period of time. This time interval will typically be less than the duration of most types of news and entertainment programs. Another problem with receiving terrestrial transmissions is that the relative distance between the aircraft and the broadcast station changes quickly as the aircraft travels along its flight path, resulting in large variations in signal strength and transmission quality. Moreover, for terrestrial transmissions which are capable of being received over long distances, the blocking effect of the earth's horizon can interfere with proper signal reception.
In co-pending, commonly-assigned U.S. patent application Ser. No. 08/569,346, filed by S. Joseph Campanella on Dec. 8, 1995, now U.S. Pat. No. 5,835,487, and in the other co-pending applications identified previously, a new global digital broadcast system is described. The system employs three geostationary satellites, each having three contiguous downlink spot beams covering large land masses. The primary intended mode of reception is a portable radio receiver, with the ability to select one of several hundred 16 kilobit per second (kbps) prime rate channels. These channels can be used individually for audio or text broadcasts, or they can be combined to form digital streams as wide as 1.5 to 2.0 megabits per second (mbps). Depending upon the mode selected, the uplink signals for these broadcasts can originate either from a central hub located at a discrete site within the uplink coverage area of a satellite, or from a plurality of individual Very Small Aperture Terminals (VSATs) distributed throughout the uplink coverage area of the satellite. Underlying the present invention is the recognition that a satellite-based digital broadcast system of this type can be used to provide real-time broadcast programs to aircraft in flight, without suffering from the disadvantages and limitations of the prior art.